Fuze device with target detecting means

ABSTRACT

A fuse device capable of producing a signal in proximity to a target in response to changes in infra-red radiation due to the presence of the target, the device having a single field of view, a device responsive to radiation in said field of view to produce corresponding electrical signals, optical means interposed between said device and said field of view and operable to discriminate against radiation outside a selected range of wavelengths and electronic means supplied with said electrical signals and having a frequency band-pass selected to reject signals having a frequency below a selected value corresponding to a selected minimum rise-time of the signals.

[ FUZE DEVICE WITH TARGET DETECTING MEANS [75] Inventor: Peter BrianGodfrey, Luton, En-

gland [73] Assignee: Hawker Siddeley Dynamics Limited,

Hatfield, 'I-Iertfordshire, England 22 Filed: Dee. 6, 1966 21 AppLNo;600,005

30 Foreign Application Priority Data Dec. 6, 1965 Great Britain..5l,7l7/65 52 us. c1 ..102/70.2 P, 250/833 H 51 Int. Cl ..F42b 5/08 58Field of Search ..102/70.2 P, 70.2; 244/3. 16; 250/833 IR [56]References Cited UNITED STATES PATENTS 3,149,231 9/l964 Ravich "244/3163,282,540 11/1966 Lipinski ..244/3.l6

FOREIGN PATENTS OR APPLICATIONS 635,43l 1/1962 Canada ..l02/70.2P

[ 1 Apr. 17, 1973 OTHER PUBLICATIONS IR System Designer Faces ManyHurdles" by Philip J. Klass, Aviation Week, Mar. 11, 1957, pp. 78-79,8l, 83, 84, 85, 89, 91 and 92.

Primary ExaminerSamuel F einberg Attorney-Karl W. Flocks [57] ABSTRACT Afuse device capable of producing a signal in proximity to a target inresponse to changes in infra-red radiation due to the presence of thetarget, the device having a single field of view, a device responsive toradiation in said field of view to produce corresponding electricalsignals, optical means interposed between said device and said field ofview and operable to discriminate against radiation outside a selectedrange of wavelengths and electronic means supplied with said electricalsignals and having a frequency band-pass selected to reject signalshaving a frequency below a selected value corresponding toa selectedminimum rise-time of the signals.

2 Claims, 13 Drawing Figures PATENTED APR 1 7 I973 SHEET 2 OF 8 FUZEDEVICE WITH TARGET DETECTING MEANS This invention relates toimprovements in fuze devices such as are used in missiles to initiateexplosion of a warhead in proximity to a target. A form of such fuzedevices respond to infra-red radiation from a source of radiation on thetarget. The radiation source may be a. near blackbody radiation from ajet pipe b. near blackbody radiation from a piston engine exhaust pipe,

0. CO hot gas radiation at about 4.4 microns wavelength d. nearblackbody radiation from kinetically heated aircraft and missilesurfaces, or

e. near blackbody radiation from engine heat conducted to aircraftsurfaces One of the problems associated with the design of such fuzedevices is that of enabling the device to distinguish between radiationfrom the sun and radiation from the target. This is frequently achievedby providing the device with two diverging fields of view and deriving ameasure of the time taken by the radiation source to pass from one fieldof view to the other. Solar radiation may then be rejected by a timegate which a duration less than that of sun signals resulting from thepitching motion of the missile and are thus discriminated against.

There exists, however, a demand for less sophisticated and lessexpensive fuze devices capable of operating in lethal proximity to atarget.

I here is considerable atmospheric absorption of the suns radiationparticularly at wavelengths towards the lower end of the range normallyof interest in detecting radiation from aeroplanes, missiles and similartargets. Furthermore, the level of that part of the suns radiationhaving a wavelength within the band which is of interest is considerablyreduced. Additionally, the entry of the sun into a fuze field of viewdue to missile pitching motion produces a signal from a radiationdetector which has a rise-time which is long compared with that producedfrom a target. Consequently, we have found it possible to devise a fuzedevice operating with only a single beam or field of view which iscapable of discriminating between the sun and a target.

According to the present invention, there is provided a fuze devicecapable of producing a signal in proximity to a target in response tochanges in infra-red radiation due to the presence of the target, thedevice having a single field of view, a device responsive to radiationin said field of view to produce corresponding electrical signals,optical means interposed between said device and said field of view andoperable to discriminate against radiation outside a selected range ofwavelengths and electronic means supplied with said electrical signalsand having a frequency band-pass selected to reject signals having afrequency below a selected value corresponding to a selected minimumrise-time of the signals.

In one application, as applied to a short range ground to air missile,it is preferred that the optical means should discriminate againstradiation outside the range of4.2 to 6.5 microns.

with advantage, the upper limit of the range is defined by a windowthrough which radiation is admitted to the device and the lower limit isdefined by an interference filter disposed in the path of radiationbetween the window and the radiation responsive device.

Desirably, the window is formed from calcium aluminate glass and theradiation sensitive device is an indium-antimonide cell. Advantageously,means is provided to cool the cell to a temperature below 0C. andpreferably of the order of 40C. The cooling means is conveniently asingle-shot system operating on the evaporation principle and embodyinga refrigerant. Means is provided to break a seal when the missile iscommitted to be launched to allow the refrigerant to boil off at ambientpressure.

The window is preferably mounted on a triangulated frame which connectsthe fuze device to the body of the missile on which it is carried, thetriangulated frame being designed so that the axial length of windowaperture is constant through 360 about the'missile axis.

The electronic means is preferably arranged to reject signals having arise-time corresponding to frequencies below c.p.s., although this canbe selected to have any suitable value according to the application inview.

The fuze device is mounted forwardly of the main body of the missile andthe electrical means is preferably mounted forwardly of the opticalsystem defining the single field of view. The electronic means ispreferably mounted on a plurality of spaced boards carried on pillars,the boards being substantially circular and of decreasing diameterconsidered in the forward direction of the missile.

One embodiment of the invention will now be describedby way of example,reference being made to the accompanying drawings in which:

FIGS. 1A, 1B and 1C respectively show spectral curves of the sunsradiation at sea-level, spectral emission curves from exhaust gases of atypical jet engine at low altitude and at 10 metres range, and aspectral response curve of the fuze device to be described.

FIG. 2 is a block diagram illustrating a fuze system according to thepresent invention,

FIG. 3 is a fragmentary perspective view of a fuze device according tothe invention embodying the system of FIG. 2,

FIG. 4 is an end elevational view of the fuze device of FIG. 3 on alarger scale,

FIG. 5 is a fragmentary section taken on the line V- V of FIG. 4,

FIG. 6 is a section taken on the line VIVI of FIG. 5,

FIG. 7 is a section taken on the line VII-VII of FIG.

FIG. 8 is a section taken on the line VIIIVIII of FIG. 5,

FIG. 9 is a circuit diagram of the electronic means of the system shownin FIG. 2,

FIG. 10 is a circuit diagram of an RF. filter embodied in the system,and

FIG. 11 is a graph illustrating the sun signal to threshold ratioplotted against missile pitch rate in /sec. for three altitudes.

As can be seen in FIG. 1A, the spectral emission of the sun falls off atsea level at wavelengths above about 4.2 microns although there is aslight increase between about 4.4 to nearly 5 microns. This falling offis due to absorption of the suns radiation by the earths atmosphere.FIG. 1B shows the spectral emission from the exhaust gases of a typicaljet engine at a low altitude and at about 10 metres range. It will beseen that this emission is significant between about 4.1 and 4.7 micronsand it follows that a fuze device must be responsive to radiation inthis range. However, in order to respond to radiation from aircraft jetpipes and piston engine exhaust stubs and also aircraft surfaces heatedby kinetic energy and conduction from engines, the range of response ofthe fuze device should be extended to include wavelengths of between 5to 7 microns. FIGS. 1C shows the spectral response of the fuze device tobe described and it will be observed that it has a response to radiationin the range of from about 4.2 to 5.5 microns.

The fuze device of this example is indicated generally at 10 in FIG. 3and is mounted forwardly of the main body 11 (FIG. 3) of the missile.

The fuze device comprises a light alloy base casting 12 (FIG. 5) whichhouses an optical assembly and a light alloy ogive-shaped spinning 13which forms the nose cone which houses electronic means to be described.The base casting 12 is pierced intermediate its length by eighttriangular apertures 14 and has a bulk head 15 forwardly of theapertures 14 which supports a photo-conductive indium antimonide cell 16over a centrally disposed aperture 17. The aperture 17 is covered by anoptical filter l8 surrounded by a rearwardly extending skirt 19. Alsomounted on the bulkhead 15 in association with the cell 16 is a singleshot cooling system of which part is shown at 20 and which operates toimprove the sensitivity of the cell 16 by cooling it to a temperature ofabout 40C. This cooling system can take any suitable form but preferablyuses a refrigerant which is allowed to boil off at ambient pressure asthe missile is launched, suitable means being provided to rupture a sealand allow the boiling off to commence immediately prior to launching themissile.

At the rear of the casting 12 is mounted an annular powered mirror 21designed to provide optical gain and to focus radiation admitted throughthe apertures 14 on to the cell 16 through the filter 18, the skirt l9preventing radiation impinging directly on the cell 16 from theapertures 14. The diagonal lattice-window structure is strong enough toallow the missile to be lifted by the nose and is therefore more thanadequate for the aerodynamic and lateral inertia loads imposed by flightmanoeuvre. The staggered window configuration provides a continuousfield of view of 360 in the transverse plane of the optical system andat the same time ensures that the axial length of the aperture isconstant throughout the 360 field of view. The apertures 14 are sealedby a frustoconical window 22 of calcium aluminate glass which seals theoptical assembly by means of rubber 0 rings 23 interposed between thewindow 22 and the casting 12. These rings 23 prevent mechanical loadsother than those produced by local aerodynamic pressure being imposed onthe window 22 and also overcome the effects produced by the differingthermal expansion characteristics of the window 22 and the casting 12.Any electrical wiring, which must of necessity pass across the window22, is loomed and clipped to the underside of the diagonals defining thewindows 14 so as not to give rise to obscuration problems.

In the optical system described, the filter 18 is selected so as only topass radiation having a wavelength above about 4.2 microns and thewindow 22 is selected to pass only radiation having a wavelength belowabout 5 .5 microns. The system therefore only allows the cell 16 to seeradiation having a wavelength between about 4.2 microns and 5.5

mlCIOnS.

The optical system is so designed that the field of view of the fuzedevice is slightly forward looking and is slightly diverging. Thus, inthis example, in any plane containing the missile axis, the fuze has afield of view the medial line of which makes an angle of about with themissile axis in the forward direction, the beam diverging so that theforward boundary of the field of view makes an angle of about 68 withthe missile axis in the forward direction and the rearward boundary ofthe field of view makes an angle of about 72 with the missile axis inthe forward direction.

The bulkhead 15 has a forwardly extending skirt 24 which is covered by aplate 25 to define a space 26 in which is disposed the cell 16, and thepart 20 of the cooling system. Also within the space 26 is an R.F.filter housing 27 carried on the plate 25. Within the spinning 13 andcarried on the plate 25 are nine substantially circular boards ofelectrically insulating material and of decreasing diameter towards theforward end of the missile. These boards are identified as boards 1 to 9and are mounted in spaced relationship on three equiangularly disposedpillars 57 carrying electrically insulating spacing collars. Boards 1 to7 carry the electronic means to be described, board 8 is left blank andboard 9 carries a contact fuze.

In some cases, a telemetry aerial installation may be provided forwardlyof the boards 1 to 9. In this case, a cable would be required to extendfrom the nose rearwardly of the casting 12. Such a cable is shown at 28and it will be appreciated that the boards 1 to 9 would each have asmall cut-out portion at their periphery to allow the telemetry cable 28to pass. The cable 28 passes through a bore 29 in the rear of thecasting 12 in which it is sealed by a sealing material as at 30. Thecable 28 also passes through the plate 25 by way of a sleeve 31 (FIG. 7)to which the metal braiding of the cable 28 is soldered. Also passingthrough the plate 25 are two leads 32 and 33 which pass the output fromthe cell to the electronic means to be described and which arerespectively connected to terminals 34 and 35 mounted on the board 1.

As can be seen in FIG. 2, the cell 16 is energised by a cell polarisingcircuit 36 which is supplied with a 35 volts power supply along a lineindicated at 37 and is mounted on board 2. The output from the cell 16is supplied to an amplifier 38 and electronic filter 39. The amplifier38 is mounted on boards 1, 4, 5 and 6 and the filter mainly on board 3.The amplifier 38 and electronic filter 39 have a combined noise figureof less than 6 dB. The filter 39 has a high-pass, high-slope designed tocut-off signals having a rise-time corresponding to frequencies belowabout c.p.s. so as to provide maximum discrimination between the signalrise rate due to the missile passing a target and that due to the sunand the missile motion. The output from the amplifier 38 and the filter39 passes to an amplitude gate 40 which is largely mounted on board 7but includes a diode MR1 (FIG. 9) carried on board 6. When there is anoutput from the gate 40 this passes to a firing circuit 41 whichincludes a silicon controlled rectifier SCRl which is mounted in the RP.filter housing 27 and which operates to switch a 6 volt supply alongline 42 from the power supply (not shown) directly to a warhead igniter(not shown) which, for firing purposes, requires 4 amps. supplied into0.5 ohms for less than a millisecond. It will be noted that this pulseof current is required to flow only once in the missile flight time,i.e. when the fuze triggers on a target at the time of nearest miss. The35 volt power supply is only required to provide approximately 1.6 wattsfrom 2 seconds before launch up to the time the fuze triggers.

The contact fuze carried by board 9 is a printed line 43 which isshattered on impact of the missile with a target and causes the siliconcontrolled rectifier SCRl to switch and ignite the warhead.

The electronic means is shown in greater detail in FIG. 9 and the RF.filter circuit is shown in FIG. 10. The RF. filter circuit is providedto ensure that any extraneous radiations picked up by the external leadsare filtered out to prevent faulty initiation of the fuze.

The electronic circuitry shown in FIG. 9 will now be briefly described.The 35 volt supply from the R.F. filter is fed along line 37 to the cellpolarising circuit 36 which comprises a plurality of series connectedresistors R1 to R6 with capacitors C1 to C5 connected in parallel. Thispolarising circuit 36 smooths the supply. The output from the cell 16appears across resistor R6 and is fed to amplifying transistor VT1followed by transistor VT2 connected as an emitter follower. A capacitorC9 connected between the collector and base electrodes of the transistorVTlprovides feedback and operates to control the frequency response ofthe transistor at the top end of the scale, i.e. the top cut. Acapacitor C connected in the emitter circuit of the transistor VTlinfluences the frequency response of the transistor at the lower end ofthe scale, i.e. the bottom cut. The output from the transistor VT2 issupplied to an amplifying transistor VT3 which is coupled to a furthertransistor VT4 by a filter network of the parallel T kind, This filternetwork is designed to provide a steep slope at the lower end of thescale i.e. at cut-on to ensure that signals having a rise-time less thanabout 150 c.p.s. are rejected. The output from the transistor VT4 issupplied to amplifying transistors VT5 and VT6 having a feedbackconnection therebetween provided by resistor R38. A capacitor Cconnected across resistor R38 influences the frequency response at thetop end of the scale and a capacitor C21 in the emitter circuit of thetransistor VTS influences the frequency response at the lower end of thescale. The output from transistor VT6 is fed to further amplifyingtransistors VT7 and VTS provided with a feedback resistor R45 acrosswhich is connected a capacitor C which influences the frequency responseat the top of the scale. A capacitor C26 in the emitter circuit oftransistor VT8 influences the frequency response at the lower end of thescale. A potentiometer RVl is provided between capacitor C25 and C26 asa gain control for controlling the sensitivity of the amplifier. Theoutput from transistor VT8 is fed to transistor VT9 which is connectedas an emitter follower and which is arranged to control the triggeringof a mono-stable circuit incorporating transistors VT) and VT11. Thecondition of diode MR1 controls the triggering of the mono-stablecircuit and a suitable bias, e.g. of 1 volt, is applied across the diodeMR1 to define a threshold value which must be exceeded by the outputfrom the transistor VT9 before the mono-stable circuit can be triggeredto initiate firing of the warhead. The mono-stable circuit VT10'and VT11is also arranged to be triggered by a break in the contact fuze 43 whichis connected between the collector electrode of transistor VT10 and thebase electrode of transistor VT11.

The R.F filter circuit shown in greater detail in FIG. 10 has sixterminals 51 to 56 connected externally of the electronic meansdescribed above and six terminals 61 to 66 associated with theelectronic means. Terminals 66 and 56 are directly connected andrepresent earth. Terminal 55 is connected to the 35 volt supply linewith terminal connected to the supply line 37. Terminals 54 and 64 arespare. Terminal 63 is connected to the emitter electrode of transistorVT9 so that a signal representing the amplifier output is available atterminal 53. Terminal 52 is connected to the 6 volt supply and throughthe silicon controlled rectifier SCRl to terminal 51 which is connectedto the warhead igniter. The switching electrode of SCRl is connected toterminal 62 which is connected to the output from the mono-stablecircuit VT10 and VT11. Thus, when the output from transistor VT9 exceedsa selected threshold value, or when the contact fuze 43 is broken, themono-stable circuit is triggered to switch the silicon controlledrectifier SCRl to the conducting condition and apply the 6 volt supplyto the warhead igniter.

It will be appreciated from the above description that the fuze devicedescribed has a single field of view of 360 about the missile axis andoperates to discriminate against rediation from the sun by both opticaland electronic filtering. The spectral band of the fuze is chosen tomake use of the high absorption of the suns radiation by the earthsatmosphere. Thus the filter 18 and the window 22 ensure that the cell 16only responds to wavelengths of between about 4.2 microns and about 5.5microns. Any radiation from the sun at low altitudes and within thiswavelength band is of comparitively small amplitude. Additionally, ifthe sun passes through the field of view of the fuze device, the'signalresulting therefrom will have a relatively slow rise-time which willcorrespond to frequencies below about c.p.s. Due to the sharp cut-offprovided by the electronic means, such signals will be rejected andcannot operate to ignite the warhead.

The response of the amplifier is chosen to make use of the differencebetween the'sight-line spin rate when the fuze beam sweeps through thetarget source and the rate at which the missile can pitch in the planecontaining the sun and the missile axis.

FIG. ll 1 shows the sun signal to threshold value plotted against pitchrate for the fuze under the following conditions:

a. the fuze is looking at the sun and the pitch plane contains the sunand missile axis,

b. the missile pitch amplitude is greater than 2 at the pitch ratestated, and

c. the sun is at its zenith for temperate climate in clear weatherconditions.

Under normal conditions of operation, missile pitch rates abovel25/second are'not expected to occur and, if the fuze field of viewsweeps through the sun during the missile trajectory, it can be seenfrom FIG. 11 that the sun signal will be below the fuze threshold.

It will be understood that although, in the example described, thewindow 22 imposes an upper limit of 5.5 microns on the wavelength of theradiation sensed by the system, this may be extended to 6.5 microns bysuitably selecting the window material. This improvement in response toradiation at these larger wavelengths provide greater capability againstkinetically heated targets. In fact the radiation wavelengths to whichthe device responds may be controlled by suitably choosing the filter l8and the material of the window 22. In some cases, it may be desirable tohave the device respond to a relatively narrow radiation band having amid-point of 4.4 microns where one is concerned, for example, in thedetection of a jet engine exhaust.

It will be appreciated that the window 22 may be bloomed internally andexternally to avoid such internal reflections as may give rise tospurious signals.

It will also be understood that the cooling achieved by the single shotcooling system is dependent upon the ambient pressure conditionsexisting at initiation of the boiling off of the refrigerant. Hence, aground launch would produce a higher temperature than a launch at higheraltitudes.

Iclaim:

l. A fuse device mounted forwardly of the main body of a missile andcapable of producing a signal in proximity to a target in response tochanges in infrared radiation due to the presence of a target, thedevice having a single field of view and including a device responsiveto radiation in said field of view to produce corresponding electricalsignals, optical means defining the single field of view and operable todiscriminate against radiation outside a selected range of wavelengths,and electronic means mounted forwardly of the optical system on aplurality of spaced boards carried on pillars, the boards beingsubstantially circular and of decreasing diameter considered in theforward direction of the missile, the electronic means being suppliedwith said electrical signals and having a frequency band-pass selectedto reject signals having a frequency below a selected valuecorresponding to a selected minimum rise time of the signals.

2. A fuze device according to claim 1 including a contact fuze carriedon one of said boards and operable on impact to generate a warheadigniting signal.

1. A fuse device mounted forwardly of the main body of a missile andcapable of producing a signal in proximity to a target in response tochanges in infrared radiation due to the presence of a target, thedevice having a single field of view and including a device responsiveto radiation in said field of view to produce corresponding electricalsignals, optical means defining the single field of view and operable todiscriminate against radiation outside a selected range of wavelengths,and electronic means mounted forwardly of the optical system on aplurality of spaced boards carried on pillars, the boards beingsubstantially circular and of decreasing diameter considered in theforward direction of the missile, the electronic means being suppliedwith said electrical signals and having a frequency band-pass selectedto reject signals having a frequency below a selected valuecorresponding to a selected minimum rise time of the signals.
 2. A fuzedevice according to claim 1 including a contact fuze carried on one ofsaid boards and operable on impact to generate a warhead ignitingsignal.